LD modules are widely used for the purpose of coupling a laser beam emitted from an LD (Laser Diode) element (semiconductor laser element) to an optical fiber. Among such LD modules, a micro-optical device disclosed in Patent Literature 1 has been known as a light-guiding device that guides a laser beam emitted from each of a plurality of LED elements to an optical fiber.
FIG. 12 is a perspective view of a micro-optical device 10 disclosed in Patent Literature 1. As illustrated in FIG. 12, the micro-optical device 10 includes a base plate 11, an LD bar 12, a cylindrical lens 13, a first mirror row 14, and a second mirror row 15.
The LD bar 12 includes a plurality of LD elements aligned along an x axis and emits laser beams in a z-axis positive direction from the plurality of LD elements, respectively. The laser beams emitted in the z-axis positive direction from the plurality of LD elements, respectively, have respective optical axes that are aligned along the x axis within a first plane parallel to a zx plane.
Note that propagation directions of the laser beams emitted from the LD elements, respectively, are dispersed in directions in a range of ±θx around the z-axis positive direction at the center. On this account, the micro-optical device 10 is arranged such that the laser beams emitted from the LD elements, respectively, are collimated by the cylindrical lens 13 that is provided so as to face an emission edge surface of the LD bar 12 (i.e., the propagation directions are converged in the z-axis positive direction).
The first mirror row 14 is a mirror row in which mirror surfaces 14a are combined. The mirror surfaces 14a are opposed to the LD elements, respectively, which constitute the LD bar 12. Each of the laser beams emitted from the LD elements in the z-axis positive direction, respectively, is reflected into a y-axis positive direction by a corresponding mirror surface 14a which is opposed to a corresponding one of the LD element. Meanwhile, the second mirror row 15 is a mirror row in which mirror surfaces 15a are combined. The mirror surfaces 15a are opposed to the mirror surfaces 14a, respectively, which constitute the first mirror row 14. Each of the laser beams having been reflected into the y-axis positive direction by the mirror surfaces 14a, respectively, is further reflected into an x-axis positive direction by a corresponding mirror surface 15a which is opposed to one of the mirror surface 14a that has reflected the laser beam.
Note that, mirror surfaces 14a and 15a that reflect a laser beam emitted from an (i+1)th LD element (as counted in a direction from an x-axis positive side to an x-axis negative side) are provided on a z-axis negative direction side of mirror surfaces 14a and 15b that reflect a laser beam emitted from an i-th LD element (as counted in the direction from the x-axis positive side to the x-axis negative side). On this account, optical axes of the laser beams reflected by the mirror surfaces 15a are aligned along a z axis in a second plane that is parallel to the zx plane. This second plain is at a position on a y-axis positive direction side of the first plane as described above.
In this way, the micro-optical device 10 functions to convert a first beam bundle made of laser beams propagating in the z-axis positive direction in which the laser beams are emitted from the LD elements constituting the LD bar 12, to a second beam bundle made of laser beams propagating in an x-axis direction into which the laser beams are reflected by the mirror surfaces 15a constituting the second mirror row 15. The second beam bundle that is to be outputted from the micro-optical device 10 (hereinafter, referred to as “output beam bundle”) is converged on an incident edge surface of an optical fiber by, for example, a lens (not illustrated).
In an LD module including the micro-optical device 10, the second beam bundle (hereinafter, referred to as “output beam bundle”) outputted from the micro-optical device 10 is converged by an F-axis converging lens. Then, the output beam bundle converged by the F-axis converging lens enters an optical fiber through an intersection of the laser beams constituting the output beam bundle, that is, through an incident edge surface provided on a focal point of the F-axis converging lens. Note that the laser beams constituting the output beam bundle, that is, optical axes of the laser beams reflected by the mirror surfaces 15a constituting the second mirror row 15 are parallel to one another.